Microwave diode mixers are well known in the art. The mixer has a port for carrying an RF signal, a port for carrying an LO signal, and a port for carrying an IF signal which is the difference between the RF and LO signal frequencies. In a down converter, the mixer receives RF and LO signals and outputs the IF signal. In an up converter, the mixer receives the IF signal and the LO signal, and outputs the RF signal. The frequencies which are output from the mixer are the modulation products which exist according to the heterodyne principle by which the mixer operates, wherein a pair of signals are applied to a nonlinear element such as a diode.